RF filters are well known in the art and are widely used for controlling and enhancing the performance of communications systems. A variety of conventional RF filters have been designed for such purposes. One common type of conventional RF filter is a stripline filter comprised of a housing and transmission lines housed therein which are both machined from a metal block by milling equipment.
Such conventional RF filters suffer from several drawbacks. First, the machined filter is both heavy and bulky, as well as expensive to manufacture. Second, the formed transmission lines must be relatively thick to resist being bowed during the machining process. This thickness results in high signal loss. Third, machined parts are often mechanically misaligned when formed which can adversely effect both filter performance, as well as the yield of acceptable devices attained from a fabrication run. Fourth, the fabrication process is slow and labor intensive. Finally, the ground planes and fastening and support structures must be relatively thick to support the transmission lines, all of which add to the weight, size and expense of the filter.
To overcome the foregoing drawback associated with transmission lines formed from metal plates, other conventional RF filters use printed wiring boards (PWB) to form the transmission lines. Such filters, however, still use a relatively thick machine formed housing, resulting in a filter which is still relatively heavy, bulky and expensive.
It is therefore an object of the present invention to provide an improved RF filter that is relatively lightweight, small in size and inexpensive to manufacture. Another object of the present invention is to provide an improved RF filter that can be fabricated in an efficient and cost-effective manner resulting in high fabrication yields. It is a further object of the present invention to provide an improved method for fabricating such an RF filter.